Conventional gas feed devices have been proposed for feeding hydrogen from a plurality of hydrogen absorbing alloy tanks to a hydrogen engine. The device proposed in Japanese Patent Laid-Open Publication No. Hei 5-254353, for example, is provided with a stop valve and a pressure sensor in the vicinity of a supply port of each hydrogen absorbing alloy tank to detect opening or closing of the stop valve by the pressure sensor.
However, such gas feed devices sometimes fail to detect the opening or closing of the stop valve. Although opening or closing of the stop valve is sensed by the pressure sensor, opening or closing of the stop valve cannot be detected if the pressure sensor malfunctions. When the pressure sensor malfunctions, the amount of hydrogen remaining in the hydrogen absorbing alloy tank or the amount of hydrogen while hydrogen is being charged cannot be easily or accurately detected.